The invention relates to molecular, inorganic glasses composed, in part at least, of thermally-stable, zero-dimensional clusters, each of which is composed of arsenic and sulfur atoms and associated with germanium atoms.
The physical structure of a glass may be characterized by its dimensionality, that is, by the number of directions in which its components extend. Thus, vitreous selenium, which is believed to consist of intertwined chains of selenium atoms, is said to have a one-dimensional structure. Likewise, glassy AS2S3, which consists of corrugated sheets of As2S3 pyramids that share corners, is described as having a two-dimensional structure. Considered in these structural terms, most oxide glasses are said to be three-dimensional.
A certain class of crystalline, inorganic compounds, known as molecular solids, have a zero-dimensional structure. This structure consists of molecular clusters in a cage-like form. As such, the clusters are repeated periodically in three dimensions, but are only bonded to each adjacent cluster by van der Waals forces. Examples of crystalline, inorganic compounds that have such a structure are known. They include arsenic sulfide, which consists of eight atom clusters designated As4S4, and phosphorous sulfide, which consists of 14 atom clusters designated as P4S10.
The possibility of an inorganic glass having such a structure has been suggested by R. Zallen. He has suggested that such a zero-dimensional structure may occur temporarily in amorphous arsenic sulfide films which have been fabricated by vapor-phase deposition. Although such structure is found in these films initially upon cooling, it is thermally unstable in that it is lost upon annealing the films.
The present invention is based on discovery that bulk, inorganic glasses can be produced that consist almost entirely of thermally-stable, zero-dimensional clusters. These novel glasses have some physical properties similar to those observed in organic plastics. However, they also exhibit other properties that more closely resemble those found in conventional, three-dimensional, inorganic glasses such as complete transparency between the visible and infrared cutoff wavelengths. These unique glasses are hereafter described in greater detail.
The invention resides in part in a molecular, inorganic glass that is resistant to devitrification, that is constituted, in part at least, of thermally-stable, i.e., persisting after annealing, zero-dimensional clusters or molecules composed of four atoms of arsenic and three atoms of sulfur, that, optionally, contains up to 12% of germanium atoms, the clusters being bonded to each other primarily by van der Waals forces, and wherein at least 95% of the composition consists essentially of, on an atomic percent basis, 42-60% arsenic (As), up to 48% sulfur (S), 0-14% selenium (Se), the content of S+Se being 37-48%, and, optionally, up to 12% germanium (Ge).
The invention further resides in a method of producing a thermally-stable, Asxe2x88x92S glass that is composed, in part at least, of zero-dimensional clusters or molecules composed of four atoms of arsenic and three atoms of sulfur, the method comprising forming a mixture of 42-60% arsenic, 37-48% S+Se wherein the Se is 0-14%, with, optionally, up to 12% germanium (Ge), and melting the mixture to form a devitrification-resistant, inorganic glass melt.
The term xe2x80x9catomic percent,xe2x80x9d as used herein, represents the actual percent of the total number of atoms present. Thus, the value given for a particular element represents the percent of atoms of that element present in a composition as compared to 100 percent for the total number of atoms in the composition.